Both carbonated and non-carbonated beverages may be stored in a frozen or semi-frozen state and dispensed in the form of a slush. Typically, frozen or semi-frozen beverages are stored in a tank, which includes a motor-driven blade for stirring and mixing the beverage stored in the tank. Refrigerant is circulated in heat exchange relationship with the tank to keep the beverage stored therein frozen or at least partially frozen. The beverage is stored under relatively high pressure (e.g., 37 psi) and is dispensed by means of a user-operable valve.
One problem associated with prior art apparatus for storing and dispensing such frozen or semi-frozen beverages is that ice will accumulate on the walls of the container, both inside and out. The apparatus typically includes a defrost mechanism for periodically defrosting the container. A defrost cycle may be initiated automatically based on a predetermined elapsed time since the last defrost cycle or it may be initiated in response to a predetermined condition, such as increased load on the blade motor, which is an indication of excessive ice buildup on the walls of the tank and on the blade drive shaft. During defrost, the dispensing valve is disabled because the beverage may be at least partially melted, which would result in a sudden blast of melted beverage at even greater than normal pressure. Therefore, there is a need to reduce the time required for defrost and to increase the time between defrost cycles.
Another problem associated with such prior art storage and dispensing apparatus is that cf excessive dispensing pressure because of the relatively high pressure under which the beverage is stored. Even when the tank is not being defrosted, opening the valve can release a sudden blast of pressurized beverage, which may result in an unpleasant surprise to the person operating the valve and may also result in loss of control of the cup or other container used by the person operating the valve to capture the beverage. Prior art solutions to this problem have generally involved using a specially designed dispensing passageway or inserting a diffuser into the dispensing passageway to "break up" the flow.
For example, U.S. Pat. No. 4,911,333 describes a specially designed dispensing passageway that directs the beverage radially outwardly toward the walls of the valve bore. Although dispensing pressure is reduced, this type of valve is subject to leakage after the valve is closed because of the beverage residue in the passageway and in the faucet portion of the valve beneath the valve seat. Another solution, as described in U.S. Pat. No. 5,487,493, uses a diffuser member to diffuse the beverage downwardly as well as outwardly as it is being dispensed, which reduces beverage residue in the dispensing faucet after the valve is closed. This approach also reduces dispensing pressure, but there may still be a sudden release of the beverage when the valve is first opened, particularly if the beverage is in a liquid state. Therefore, there is a need to prevent a sudden surge of pressurized beverage when the dispensing valve is opened.
Yet another problem associated with prior art storage and dispensing apparatus is that when a frozen beverage is dispensed, small particles of ice may accumulate around the valve stem and prevent fluid-tight engagement of the valve stem with the valve seat, which may result in valve leakage. Further, when the beverage is a fruit drink, such as a strawberry drink, seeds from the small pieces of fruit present in the drink may also accumulate around the valve stem and further prevent fluid-tight engagement of the valve stem with the valve seat. Therefore, there is a need to remove ice and seed residue from the valve stem and seat so as not to interfere with valve closure.